Bubble detectors have become an important safety feature in many applications including industrial and medical applications. For example, in medical applications, if air is introduced into the bloodstream via an infusion tube, an air embolism may occur. The effects of an air embolism may range from little or no effect to death, typically depending on the amount of air which is introduced. Industrially, it is often desirable to detect the presence of air in a fluid stream to more accurately dose the fluid or to avoid introduction of air into a system. Therefore, it is often useful to automatically detect bubbles.
In the medical field, air bubble detection is often important. Typical applications include dialysis, enteral feeding, and intravenous introduction of fluids. In these situations, the greater the volume of air, the greater could be the risk of harm.
Current bubble detectors send ultrasonic signals through a fluid to detectors and measure amplitude changes on the received signal. The optimum ultrasonic frequency for detection is often different for different situations, as the particular detector, tubing, or fluid may affect the transmission of the signals. Thus, some bubble detectors sweep the entire possible spectrum of ultrasonic frequencies on each pass to reduce the risk of failure in bubble detection. Sweeping the entire spectrum typically results in time spent scanning for bubbles using less than optimal frequencies. The optimum frequency for bubble detection may be affected by piezoelectric crystal proportion, composition, construction tolerances and dynamic factors such as temperature, tubing composition, fluid composition, and the coupling between the sensor and the tube.
False alarms have become a problem in bubble detection. These can be caused by microbubbles that stick to a wall, bubbles that oscillate back and forth in front of a sensor, the decoupling of tubing, etc. False alarms may decrease the trust in the system and increase the workload of staff, and may cause problems or delays in dosing of medication or the like.